The present invention relates to an ultraviolet-curable organopolysiloxane composition, more particularly, to an organopolysiloxane composition having no corrosiveness and no offensive odor and which is curable by irradiation with ultraviolet light into a gel-like material having stickiness which is useful, for example, as an encapsulating and potting agent in electronic components.
Gel-like materials obtained by curing an organopolysiloxane composition are widely used as a potting agent and adhesive in various kinds of electronic components such as hybrid ICs and the like by utilizing their low elastic modulus and high adhesive bonding strength.
The crosslinks forming such an organopolysiloxane gel are typically obtained by the addition reaction between silicon-bonded vinyl groups in an organopolysiloxane and silicon-bonded hydrogen atoms in an organohydrogenpolysiloxane in the presence of a platinum catalyst. It is usual that an organopolysiloxane composition for obtaining an organopolysiloxane gel by the addition reaction is heated at a temperature of, for example, 80.degree. C. to 150.degree. C. in order to obtain a practical velocity of the reaction. This temperature of heating to accelerate curing of the organopolysiloxane composition is sometimes too high when the organopolysiloxane gel is used in an electronic component because certain electronic devices cannot withstand such an elevated temperature. Another problem in an organopolysiloxane composition of this type is poisoning of the platinum catalyst when the composition is contacted with a phosphorus- or sulfur-containing compound or an ionic compound of a heavy metal such as tin, antimony, mercury, bismuth and the like, to cause loss of the catalytic activity so that the composition can no longer be cured even by heating. Drawbacks are sometimes caused therefore when the organopolysiloxane composition is contacted with a solder alloy or a soldering flux indispensably used in the assemblage works of electronic components. This problem is one of the factors which limit the applicability of the composition in the electronic industry.
In addition, the curable organopolysiloxane composition of the above mentioned type has another serious defect in that the volume shrinkage of the composition in curing by heating is considerably large so that cracks and fissures are sometimes formed in the mass of potting gel, especially when the mass is large.
In view of the above mentioned problems and disadvantages in the conventional organopolysiloxane compositions for a crosslinked gel, it is eagerly desired in the electronic industry because of a recent trend toward compounding of electronic parts and devices to develop an improved curable organopolysiloxane composition capable of giving a gel-like material upon curing without the problems and disadvantages in the prior art.
In this regard, the inventor has conducted extensive investigations to develop a curable organopolysiloxane composition which meets the above mentioned requirements and previously proposed an organopolysiloxane composition which comprises an organopolysiloxane having, in a molecule, at least one silyl-substituted ethyl group represented by the general formula EQU [CH.sub.2 .dbd.CR.sup.1 --CO--O--(--CH.sub.2 --).sub.b --SiR.sup.2.sub.2 --O--].sub.a R.sup.2.sub.3-a Si--C.sub.2 H.sub.4 --, (I)
in which R.sup.1 is a hydrogen atom or a methyl group, R.sup.2 is an optionally substituted monovalent hydrocarbon group and the subscripts a and b are each 1, 2 or 3, and a photopolymerization initiator, which composition is useful for use in electric and electronic components since the composition is readily cured by irradiation with ultraviolet light into a rubbery elastomer and is free from the problem of catalyst poisoning. The organopolysiloxane composition of this type, however, is not always quite satisfactory as a potting or sealing agent of electric and electronic components because the composition after curing has no adhesiveness to the substrate surface on which it has been cured.